1. Field of the Invention
This invention pertains generally to test apparatus and, more particularly, to a test apparatus for testing an arc fault circuit interrupter, such as, for example, an arc fault circuit breaker.
2. Background Information
Arcing is a luminous discharge of electricity across an insulating medium, usually accompanied by the partial volatilization of electrodes. An arc fault is an unintentional arcing condition in an electrical circuit. Arc faults can be caused, for instance, by worn insulation between adjacent bared conductors, by exposed ends between broken conductors, by faulty electrical connections, and in other situations where conducting elements are in close proximity.
Arc faults in systems can be intermittent since the magnetic repulsion forces generated by the arc current force the conductors apart to extinguish the arc. Mechanical forces then bring the conductors together again in order that another arc is struck.
Circuit interrupters include, for example, circuit breakers, contactors, motor starters, motor controllers, other load controllers and receptacles having a trip mechanism. Circuit breakers are generally old and well known in the art. Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which is heated and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system. An armature, which is attracted by the sizable magnetic forces generated by a short circuit or fault, also unlatches, or trips, the operating mechanism.
Recently, there has been considerable interest in providing protection against arc faults. Because of their intermittent and high impedance nature, arc faults do not generate currents of either sufficient instantaneous magnitude or sufficient average RMS current to trip the conventional circuit interrupter. Even so, the arcs can cause damage or start a fire if they occur near combustible material. It is not practical to simply lower the pick-up currents on conventional circuit breakers, as there are many typical loads, which draw similar currents and would, therefore, cause nuisance trips. Consequently, separate electrical circuits have been developed for responding to arc faults. See, for example, U.S. Pat. Nos. 5,224,006; and 5,691,869.
For example, an arc fault circuit interrupter (AFCI) is a device intended to mitigate the effects of arc faults by functioning to deenergize an electrical circuit when an arc fault is detected. Non-limiting examples of AFCIs include: (1) arc fault circuit breakers; (2) branch/feeder arc fault circuit interrupters, which are intended to be installed at the origin of a branch circuit or feeder, such as a panelboard, and which may provide protection from ground faults (e.g., greater than 40 mA) and line-to-neutral faults (e.g., greater than 75 A); (3) outlet circuit arc fault circuit interrupters, which are intended to be installed at a branch circuit outlet, such as an outlet box, in order to provide protection of cord sets and power-supply cords connected to it (when provided with receptacle outlets) against the unwanted effects of arcing, and which may provide protection from line-to-ground faults (e.g., greater than 75 A) and line-to-neutral faults (e.g., 5 to 30 A, and greater than 75 A); (4) cord arc fault circuit interrupters, which are intended to be connected to a receptacle outlet, in order to provide protection to an integral or separate power supply cord; (5) combination arc fault circuit interrupters, which function as either a branch/feeder or an outlet circuit AFCI; and (6) portable arc fault circuit interrupters, which are intended to be connected to a receptacle outlet and provided with one or more outlets.
UL 1699 is a specification that governs the performance of AFCI products including branch/feeder type (AVZQ); outlet circuit type (AWCG); portable type (AWDO); cord type (AWAY); and combination type (AWAH) AFCIs.
UL 1699 requires that AFCIs be tested with a series of “masking load” configurations. However, switching between these multiple test configurations is tedious and repetitious and, thus, is prone to error.
UL 1699 also requires that a series of “masking tests” be conducted with the following loads: (1) a vacuum cleaner; (2) one or more electronic switching mode power supplies; (3) a capacitor start (air compressor type) motor; (4) a 1000 W electronic lamp dimmer load and a 600 W electronic lamp dimmer load (which must be tested separately); and (5) two 40 W fluorescent lamps plus an additional 5 A resistive load.
FIGS. 1-4 show test configurations A-D, respectively. The series of “masking tests” for each load involves these four test configurations: (1) configuration A: the arc fault tester 2 (i.e., arc generator) is in series with the masking load 4; (2) configuration B: the masking load 4 is in parallel with the arc fault tester 2 which is in series with a 5 A resistive load 6; (3) configuration C: the 5 A resistive load 6 is in parallel with the arc fault tester 2 which is in series with the masking load 4; and (4) configuration D: the arc fault tester 2 is in series with the parallel combination of the 5 A resistive load 6 and the masking load 4. In all of the test configurations A-D, a power source 8 is upstream of the line terminal 10 and the line neutral terminal 12 of the line side of an arc fault circuit interrupter (AFCI) 14.
As shown in FIGS. 1 and 4, the load terminal 16 and load neutral terminal 18 are on the load side downstream of the line side of the AFCI 14. The terminals 16 and 18 are respectively electrically connected to the line terminal 20 and the neutral terminal 22 of the arc fault tester 2. The ground terminal 24 of the arc fault tester 2 is electrically connected to a ground 26 associated with the power source 8.
UL 1699 requires 24 unique test configurations (i.e., 6 test loads×4 test configurations=24 test configurations). The tests themselves are relatively simple and quick, but changing between the many test configurations requires plugging and unplugging of various loads, which is tedious, repetitious and time-consuming. It is also easy to configure a test setup incorrectly, which may require repeated testing effort.
Furthermore, if the entire test sequence is performed with three different samples of each load type in order to further check compliance (e.g., without limitation, vacuum cleaners from three different manufacturers; compressors from three different manufacturers), then the total count of test configurations becomes 72 (=24×3).
Moreover, if a particular AFCI (e.g., AFCI 14) under test fails to comply with one or more of the tests, then the AFCI manufacturer must then fix the problem and repeat the test sequence discussed above, in order to ensure that the problem has been fixed and that no new problem(s) have been introduced.
The setups for the various “masking test” configurations required by UL 1699 are repeated many, many times during development, manufacture and testing for an AFCI. Clearly, there is an opportunity to reduce effort associated with testing by simplifying the masking test configuration setup process.
Accordingly, there is room for improvement in test apparatus for testing an arc fault circuit interrupter.